Hi all thanks for reading this OK my problem is that when I start my PC up it goes to boot up win xp but then restarts at first I thought it was the hard drive so I formatted it but still the same prob so you used the hard drive in my other PC and it works fine so I then tried another mother board in the PC and it is doing the same thing could this be due to a short with the mother board and the case??

You was able to put the drive in another computer and reinstall windows and have it work there? Or plug the drive into an identical machine and have it work as-is.

A hosed up windows installation can do that most times.

Yes I put the drive in to other PC formatted it and it worked fine then I took the drive out put it back in other PC formatted it again and the same thing keeps happing it goes to boo and the PC restarts

Are these PC's generic enough you can swap a power supply from the other to check it out? This doesn't work with a lot of small form factor computers.

No I cannot swap psu as on is a long flat psu and other is standard atx

It sound's like your powersupply is failing

Test your memory with Memtest86 from a boot floppy if your machine has a floppy drive. There is a cd iso version but I hate burning a 700mb cd for 2mb program (cd-rw maybe). You can also try one stick at a time in the first slot (if you have more than one stick in there anyway) to see if you can manually identify a bad memory stick.e

That is a good idea

Double check all of your connections inside the case and if you can clean all of the fans and the cpu heatsink and apply a new coat of thermal paste to it.

Also go into bios and turn on your verbose settings so you can see what the machine is doing when trying to boot up.